In general, the ceramic structural body such as a ceramic honeycomb structural body and the like formed by piercing a plurality of through-holes in the longitudinal direction of the member in parallel to each other is used as a filter for purifying exhaust gas discharged from vehicles, factories and the like.
This ceramic structural body has such an end face that the open-close condition of the through-holes shows a checkered pattern (the state that adjacent through-holes are alternately in the open-close condition). That is, these through-holes are sealed at either only one of their end faces, and adjacent through-holes are opened or closed from each other to form the checkered pattern. Therefore, when one through-hole is opened at one end face, the other end face is sealed, while the adjacent through-hole thereto is sealed at one end face and opened at the other end face.
Moreover, the ceramic structural body is such a porous body that when a gas to be treated is flown from either one end face of each of the above through-holes, the treated gas enters into an adjacent through-hole passing through porous partition walls on the way toward the other end face and then discharges out from such other end face. That is, the ceramic structural body is made possible to mutually pass the gas through the partition wall separating the through-holes. Therefore, the gas to be treated easily passes into the other through-hole in the structural body, so that the gas passes through different through-holes at the inlet side and outlet side.
Therefore, when the exhaust gas is passed through the above ceramic structural body, particle substances (particulate) in the exhaust gas are caught and purified in the partition wall portion while passing the exhaust gas flown from one-side end face through the partition wall toward the outlet port. With the purifying action of the exhaust gas, the ceramic structural body degrades the pass of the gas because the particulate is collected and accumulated in the partition wall at the inlet port side to gradually create clogging. Therefore, the ceramic structural body requires a treatment for periodically burning and removing the particulate accumulated on the partition wall, which results in the clogging, by a heating mechanism such as burner, heater or the like (hereinafter simply referred to as "regeneration").
The above ceramic structural body, however, causes nonuniform temperature distribution inside the structural body due to local heat generation accompanied with nonuniform heating process and abnormal burning of particulate, thermal shock given by sudden temperature change of exhaust gas and the like so as to bring about the action of thermal stress. As a result, the above ceramic structural body has encountered such problems that crack generation and hence molten loss are invited and finally led to breakage so as to impede collection of particulate.
On the contrary, hitherto, as means for solving the above problems, there has been proposed, for example, a method for decreasing thermal stress acting on a ceramic structural body by dividing the ceramic structural body into a plurality of ceramic members on the face perpendicular to the axis or the face in parallel with the axis (see JP-A-60-65219). Moreover, there has been proposed a divided ceramic structural body having improved property for sealing the exhaust gas by inserting a non-adhesion sealing member in a gap produced between the mutual ceramic members in this divided-type ceramic structural body (hereinafter referred to as "divided ceramic structural body") (see JU-A-1-63715).
According to the above respective proposals, the divided ceramic structural body can liberate thermal stress observed in a one-piece ceramic structural body owing to the use of the above sealing member.
However, the sealing member is non-adhesive, so that the ceramic members cannot be firmly joined to each other. Therefore, the above divided ceramic structure body according to the conventional technique was required to have a restraint force for uniting these ceramic members to maintain the form of a one-piece structural body. Therefore, as means for giving this restraint force, there has hitherto been used an arrangement of a thermally expansive heat insulator or an application of the thermally expansive heat insulator as an inner sealing member.
However, the above non-adhesion sealing member and the thermally expansive heat insulator are poor in the durability to heat in the regeneration and repetition of oscillation generated from an internal-combustion engine. Therefore, the sealing member proceeds the degradation of volume shrinkage and strength to lower the sealing property, while the thermally expansive heat insulator has a problem to rapidly lower the restoring force after volume expansion.
Therefore, the above divided ceramic structural body has lost force for supporting a plurality of ceramic members constituting this structural body, and decomposed and dispersed by the pressure of the exhaust gas. Moreover, even if a reinforcing member is arranged at an end face at an outlet side of the gas, it is difficult to prevent the degradation of the sealing member, and it is desired to improve the durability.
Particularly, in order to form a large-size divided ceramic structural body, a larger restraint force is required, the combination of the conventional non-adhesion sealing member and thermally expansive heat insulator cannot deal with from the beginning, so that a structural body is not obtained that can withstand stress to be practically useful.
Under the above circumstances, the inventors have previously proposed "EXHAUST GAS PURIFYING APPARATUS AND STRUCTURAL BODY THEREOF" with the use of a sealing member consisting of ceramic fiber, silicon carbide powder and inorganic binder by improving the sealing member constituting the divided ceramic structural body as means for overcoming the problems inherent to the above conventional technique (see Japanese Patent Application No. 5-204242).
According to this proposal, a plurality of ceramic members are joined to each other through such a sealing member, so that it is possible to improve the durability of the divided ceramic structural body to a certain extent.
However, the sealing member tends to easily cause migration (phenomenon of moving a binder with drying and removal of a solvent) when it is filled and cured between the mutual ceramic members. Therefore, the seal layer formed by curing the sealing member becomes brittle.
That is, the inorganic binder constituting the above sealing member acts to firmly join the ceramic member to the seal layer and to join an intersect point of three-dimensionally crossed ceramic fibers as an important element for developing stress buffering function of the seal layer. However, the inorganic binder moves from the inside of the seal layer to the joint face with the ceramic member through the migration produced in the course of drying and curing, whereby the joint force at the intersect point is decreased, and hence the strength of the ceramic structural body itself is lowered, so that the desired durability could not be satisfied.
Furthermore, the silicon carbide powder constituting the sealing member also moves with the above migration to bring about the lowering and nonuniformity of thermal conductivity, which results in the lowering of the regeneration efficiency of the ceramic structural body.
On the contrary, there is considered a method of improving the durability of the structural body by controlling the migration. However, this method takes a long time for drying and curing the sealing member ant undesirably degrades the productivity.
As mentioned above, the conventional divided ceramic structural body still leaves room for improvement with respect to durability and the like as a ceramic structural body.